Coronary artery bypass is one of the most widely practiced procedures for the treatment of patients with coronary atherosclerosis, yet a simple and rapid method for assessing the effectiveness of the procedure while it is being performed is not currently available. It would be extremely useful if a direct measurement of regional myocardial blood flow (rMBF) could be made prior to the closing of the chest so that the need for any pharmacologic or surgical intervention could be identified during the procedure. We propose to develop a practical, cost effective protocol to provide this data. The approach is based on nuclear medicine techniques using xenon-133 and a miniaturized, solid state detection system which would be suitable for use in the cardiac operating room. RMD Inc., in collaboration with Bowman Gray School of Medicine, has conducted a Phase I research program which demonstrated the feasibility of this concept. We therefore propose to complete the research required to develop a fully functional clinical prototype instrument and the medical protocol for its use in performing rMBF during surgery.